In a large bowl mix together ground beef, egg, breadcrumbs, pepper, salt, onion powder, garlic powder, and Worcestershire sauce.
Form into 4 balls and flatten into patties and set aside.
In a bowl mix cornstarch, beef broth, and sherry, set aside.
Heat oil in a large skillet over medium heat, add patties and onions and fry until the patties are nicely browned, about 4 minutes per side.
Transfer patties to a plate and cover to keep warm.
Add cornstarch mixture to the skillet and simmer over medium-high heat for 4 to 6 minutes, or until the gravy thickens.
Turn the heat to low, return the patties to the skillet, and simmer for another 8 to 10 minutes.
Serve sprinkled with chopped fresh parsley.